In the existing commercial preparation process of polyolefin, Ziegler-Natta catalysts of titanium or vanadium compounds have been widely used, and although the Ziegler-Natta catalyst has high activity, it is a multi-active site catalyst and thus the molecular weight distribution of the produced polymer is wide and the compositional distribution of comonomers is not uniform, and thus, there is a limit to securing of desired properties.
Thus, recently, a metallocene catalyst in which a ligand comprising a cyclopentadiene functional group is bound to a transition metal such as titanium, zirconium, hafnium, etc. has been developed and widely used. The metallocene compound is generally activated with aluminoxane, borane, borate or other activators before use. For example, a metallocene compound having a ligand comprising a cyclopentadienyl group and two sigma chloride ligands uses aluminoxane as an activator. Such a metallocene catalyst is a single site catalyst having one kind of an active site, and is characterized by narrow molecular weight distribution of the produced polymer. Thus, since polyolefin polymerized with a metallocene catalyst has narrow molecular weight distribution, in case applied for some products, productivity was remarkably lowered due to extrusion load, etc., and thus, field application was difficult.